Flat sheet membranes are made by casting a dope onto a substrate. The substrate may be, for example, a woven or non-woven fabric. The dope is cured into a solid membrane after casting. The curing mechanism may be, for example, interfacial polymerization or non-solvent induced phase separation. The resulting flat sheet membrane may have pores in a range from reverse osmosis to microfiltration. In one example described in U.S. Pat. No. 5,626,752, membrane filter elements are stacked atop one another to form a stack. The stacked units are sequentially arranged in a housing. A flow medium flows in sequence through the stacked units. Each of the membrane filter elements in the stack has a stabilizing element positioned between outer membrane elements.
US 2011/0253624, entitled Anaerobic Digester-Membrane Bioreactor for Treating a Waste Stream, describes an anaerobic reactor coupled with a membrane separation unit. Mixed liquor is pumped from an intermediate portion of the reactor, where the concentration of solids is relatively low, to the membrane separation unit. The mixed liquor is separated by the membrane unit into a permeate stream and a retentate stream. The retentate stream is pumped back to the anaerobic reactor and mixed with the mixed liquor in the reactor. Mixed liquor and relatively heavy solids are pumped from the bottom of the anaerobic reactor to a hydrocyclone. A stream concentrated with heavier solids is sent from the hydrocyclone to a dewatering unit. A lighter solids stream is sent from the hydrocyclone back to the anaerobic reactor. The membrane separation unit uses cross flow tubular membrane modules. A membrane feed pump forces mixed liquor and a recycled portion of the retentate under pressure through the insides of the membranes.